In 2001, more than 90 countries signed the Stockholm Convention on Persistent Organic Pollutants (POPs), committing to eliminate the use of 12 POPs of greatest concern to the health of the global community. POPs are lipophilic chemicals that persist in the environment, accumulate in the food chain and human adipose tissues, and are likely endocrine disrupters. Dichlorodiphenyltrichloroethane (DDT) was used as recently as 2000 in some countries, such as Mexico, and continues to be used in others for malaria control. Some are advocating their increased use. Animal studies indicate that DDT is a neurodevelopmental toxicant and we have recently shown that DDT is associated with mental deficits in two-year old children. As some of these POPs are being discontinued, new chemicals with endocrine disrupting properties are increasing in use. Polybrominated diphenyl ethers (PBDEs) are flame retardants used in textiles, furniture, and electronic products with increasing use and human exposure. Animal studies suggest that pre- and post-natal PBDE exposure causes decrements in learning and memory, and hyperactivity. Mechanisms for these effects may include thyroid hormone disruption. Recent studies have documented widespread PBDE exposure to humans, with higher levels in the United States (U.S.) compared to Europe. Only one small study (n=9) in humans has examined the relationship of pre- or post-natal PBDE exposure and thyroid function, and no studies have examined the relationship with human neurodevelopment or whether populations with higher levels of both DDT and PBDE are more adversely affected. We propose to examine the relationship of PBDE exposure, DDT exposure, and their interaction on neurodevelopment of children, and whether PBDE exposure is associated with maternal and neonatal thyroid function. We will utilize the rich data and biorepository already collected as part of the CHAMACOS project, the keystone project of the NIEHS/EPA-funded Center for Children's Environmental Health Research at UC Berkeley. This longitudinal birth cohort study is a community-based participatory project investigating in utero and postnatal exposure to pesticides and other environmental toxicants and children's health. The CHAMACOS children, whose mothers primarily immigrated from Mexico to the agricultural Salinas Valley in California, received relatively high exposure to DDT and DDE (DDT/E) in utero and are likely exposed to high levels of PBDE as they grow up in the U.S. By comparison with children living in areas of Mexico where the CHAMACOS mothers originated, we will determine the role of migration in exposure to PBDEs and DDT. The proposed study will address US EPA's data gaps in the regulation of PBDEs and the goals of NIEHS strategic plan to focus on underserved populations exposed to high concentrations of environmental agents within a broader global perspective.